Why doesn't this switch return a value?

using System;

public class RBOleDb
{
	public string DbType { get; }
	public string DbDataSource { get; }
	public string DbPath { get; }
	public string DbProvider { get; }


	/// <summary>
	/// Use this for connections to files, such as MS ACCESS, EXCEL, etc.
	/// </summary>
	/// <param name="file_path">Path to Database</param>
	public RBOleDb ( string file_path )
	{
		DbType = System.IO.Path.GetExtension ( file_path ).Replace ( "." , "" ).ToUpper ( );
		DbPath = file_path;
		DbDataSource = file_path;
	}


	public string GetProvider ( )
	{
		string result = "";
		switch ( DbType )
		{
			case "MDF":
				result = "SQLNCLI11";
				break;
			case "MDB":                   // return "Microsoft.Jet.OLEDB.4.0";
			case "ACCDB":
			case "XLSX":
			case "XLS":
			case "DBF":
				result = "Microsoft.ACE.OLEDB.12.0";
				break;
			default:
				result = "!!UNABLE TO DETERMINE PROVIDER!!";
				throw new ArgumentException ( $"DbType has a value of {DbType}, which is not valid.  RBDataOleDb clould not determine what database provider to use when connecting to database" );
		}
		return result;
	}
}

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Ricks_Class_Testing
{
	class Program
	{
		static void Main ( string[ ] args )
		{
			string mdb = $@"D:\FIRECOMM\Ricks Dallas D Drive\db\COUNTY DATA\statecounty00.MDB";

			RBDataOleDb db = new RBDataOleDb ( mdb );
			Console.WriteLine ( db.DbType );
			Console.WriteLine ( db.DbPath );
			Console.WriteLine ( db.DbProvider );
		}
	}


}